Well mining method



'SPL `15 1970 .uoBLncczlv ETAL 3,528,513v

WELL MINING METHOD Filed Aug. 10. 196'? f H63 Y 1 l 1 l l l 1 1 1 4 111 111m INVENTOR. 4

JOHN R. JACOBUCCI BY WILLIAM ZWENNEBORG United States Patent Office 3,528,513 Patented Sept. 15., 1970 3,528,513 WELL MINING METHOD John R. .Iacobucci, Norwalk, Conn., and William Z.

Wenneborg, Washington, N.., assignors to FMC Corporation, New York, N.Y., a corporation of Delaware Filed Aug. 10, 1967, Ser. No. 659,617 Int. Cl. E21b 11/02 U.S. Cl. 175-20 3 Claims ABSTRACT OF THE DISCLOSURE A well for use in the well mining of granular ore, wherein the well casing must be in pressure-tight relation to the earth formation, is sunk by driving an openend casing into the ground until one of more hard strata are reached, vdrilling the core Within the casing and continuing drilling through such hard strata to form a drill-hole therethrough, driving the casing through the drilled hole, and continuing to drive the casing through the earth formation until it reaches the granular ore.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to the well mining of a granular ore, and specifically, to a method for preparing a well for use in this mining technique.

Description of the prior art Granular ore can be mined by a technique in which a well is sunk to the granular ore and the ore mined through the Well by a mining tool; this tool sends a jet of water into the ore, thereby forming a slurry of ore in Water, and the ore slurry is recovered through a pipe in the well. The recovery is accomplished by forcing the ore slurry up through the well 'f by maintaining a higher air pressure within the well, including the cavity formed by removal of ore slurry, than that external to the well. The higher air pressure in this system assists in raising the ore slurry upwardly for recovery at the surface.

It is of course critical in this mining technique that the well and cavity be capable of holding air pressure. The cavity which is formed by removal of ore is structurally supported in part by the higher pressure (or air bubble) therein than that outside the Well; leaks around the casing would make it impossible to hold such a pressure.

Accordingly, it has been considered necessary to go through an elaborate and expensive series of steps in preparing a well for mining. In preparing such 4a well, a hole is drilled down to the ore formation utilizing inhibited mud to maintain the Well hole open and to raise the cuttings. Casings are placed in the well and cement is forced downward into the casing hole. When the cement reaches the end of the lowest casing, it flows under the casing lip and commences to rise and to fill the annulus formed by the earth lwall of the well and the exterior casing wall. Cement is forced into the casing hole until the cement in the annulus rises to the surface or at least until a substantial length of the annulus is filled with cement,

and allowed to set. Cement that remains within the casing is drilled out and drilling is continued until the hole is reestablished to the granular ore zone. The remaining cement in the annulus forms a pressure-tight seal between the earth Walls of the well and the outer surface of the casing. It has been considered necessary to use this cement seal in order to provide a pressuretight seal.

A mining tool is then lowered to the bottom of the casing and the granular ore is slurried by a jet of water which issues from the mining tool. Dislodged ore in slurry form is carried up, along with the injected water, through the casing to the surface.

The prior method, therefore, is expensive in that a long period is required to cement the casing in the previously drilled Well hole and subsequently to remove the cement that remains Within the casing. Also, during the cement-pouring stage, some cement may flow into the porous, granular ore formation, and when set, plug the system. Furthermore, once the casing has been cemented in place, it remains fixed and cannot be removed or reused. These casings are expensive, particularly Where deep Wells are required.

As a 'res-ult, there is a need for a more rapid, less expensive means for sinking a well for use in well mining, which will permit the casing to be withdrawn after use and used in other wells, yet which will provide for easy installation of the well casing and provision of a pressure-tight system Within which a substantial air pressure may be maintained in order to sustain the air bubble necessary for eiiicient jetting in slurry mining, and furthermore to assist in recoverey of slurrie-d ore.

SUMMARY OF THE INVENTION We have now found that a well can be sunk for use in the well mining of granular ores by driving an openend casing into the ground until it contacts one or more hard strata, drilling out the earth core within the casing, drilling through any hard stratum, driving the casing through said hard stratum, and continuing to drive the casing which is in a pressure-tight relationship with the earth in contact with the outer surface of the casing.

BRIEF DESCRIPTION OF THE DRAWING In the drawing there are illustrated cross-sectional views of the casing and of the earth formation during the operation of the present invention; FIGS. 1, 2. and 3 show the sequential steps which are carried out in penetration the casing through a hard stratum.

DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENTS In the following detailed description of the invention, the process will be described with reference to mining granular phosphate ore. However, it should be understood that a phosphate ore is only illustrative of one embodiment and that substantially the same technique can be used to mine other granular ores.

In the practice of the present invention, a section of open-end casing is lirst driven into the ground by conventional driving means. The driving means may Ibe of the sonic or other vibration type or of the impact type.

Vibration-type drivers vibrate vertically at frequencies typically on the order of about 1,000 cycles per minute atan amplitude of about 1/2 inch and can deliver thrusts on the order of about 45 tons/ cycle. After a section of the` casing has been driven down, a second casing is fitted above the initial casing and attached eitherby threaded, screwed joints or by welding the pipe connections together. The attached casing is then driven to substantially its full length into the ground. The above driving technique is effective in driving casings through sandy, dirt formations, Ibut not through hard clay or rock formation. When these are encountered, driving of the casing is stopped and a drill is lowered into the casing and the earth core within the casing is drilled out. When the drill reaches the hard clay or rock formation at the end of the casing, drilling is continued in order to penetrate the hard clay or rock formation. After the hard stratum has been completely penetrated by the drill, drilling is discontinued and the drill is raised from the casing. Thereafter, driving of the casing continues through the drilled hole in the hard formation and into the sub-strata.

When the bottom casing reaches the granular phosphate ore formation, driving of the casing is stopped. A hydraulic jet is then lowered down the casing and a water stream from the jet, under high pressure, is used to carve cavities in the granular ore stratum. During the use of the water-jet, air pressure is applied within the casing and underground in the cavity that is carved out by the water-jets. The super-atmospheric pressure serves two purposes. Initially, it supports the overburden in order to avoid caving and aids in raising the slurry of water and phosphate ore from the underground cavity, and maintains an air bubble or cavity which is employed in the slurry-mining technique. As mining lproceeds, the underground cavity becomes larger and the pressure must Ibe maintained to avoid caving. For this reason a pressuretight seal must be maintained between the casing and the fromation which contacts the outside of the casing.

In the present process the driving technique forms a seal between the casing and the earth formation by virtue of the compressive and elastic nature of the earth formation, thus eliminating the need for a cement seal. When the mining cavity becomes so large that mining efficiency is decreased below acceptable levels, the water-jets are removed and the casing is pulled up by means of a vibratory puller, preferably the device` used to drive it, if a vibrating hammer is used, a crane or other device able to exert sufficient force to pull the casing out of the ground. Since the casing is not cemented into the ground, removal of the casing can readily be achieved.

The present process has several advantages over conventional procedures for sinking wells in which cement is used to seal the casing in the wall. One prime advantage of the present process is that substantially decreased drilling times are required to sink a well. This is because time-consuming steps such as cement mixing, cementing, waitin-g for the cement to dry, and drilling out the cement are obviated. Further, the present process obviates the need for large quantities of inhibited mud which are commonly used in drilling since most of the drilling which is done in the present process takes place inside the driving casing; therefore, protection of the earth formation and of the well hole is not necessary.

The present process also is much less costly than the conventional system because the use of cement, and al1 of the necessary equipment to mix, handle and pour the cement is eliminated. Further, the casings can be extracted and recovered in the present process because they need not be cemented in place.

In the attached drawing the operation of the present invention is illustrated by cross-sectional views. More specifically, in FIG. 1 an open-end casing has been driven by means of a vibration-type driver 2 into a sandy or dirt formation 6 until a hard stratum of clay or rock has been reached. After driving casing 4 to refusal, the

vibration-type driver 2 is removed and a drill 10 is lowered into the casing 4 by means of drill shaft 12, and the earth core within the casing is drilled out. In FIG. 2, drilling is continued Ibeyond casing 6 until a drill hole has been bored through the hard clay or rock formation 8. Thereafter the drill 10 is removed via drill shaft 12, and the vibration-type driver 2 is then replaced on the casing 4. In FIG. 3, driving is then continued until the casing penetrates the drilled hole through stratum 8 and continues to penetrate through the sandy or dirt formation 6 beneath the hard clay or rock stratum 8.

The following example is given to illustrate the present invention and is not deemed to be limiting thereof.

EXAMPLE 1 A well Was sunk in a North Carolina granular phosphate bed as follows: The first joint of a casing, twenty-inches in diameter, having Walls 1/2 inch thick and a length of twenty feet, was lifted by a crane and the open end was placed in a pre-dug, three-foot hole 20 inches in diameter. To the top of the casing was attached a Fosters Model 2-50 hammer. The hammer, which weighed about 61/2 tons, consisted of eccentrically loaded shafts driven by two 50 horsepower electric motors. The shafts were synchronized such that the horizontal impulses were canceled out and the device vibrated vertically at a frequency of about 1,000 cycles per minute at an amplitude of 1/2 inch. About 46 tons of thrust were delivered during each cycle.

Upon connection of the hammer to the casing the initial joint of casing was sunk in less than one minute. A second joint of casing also having a diameter of 20 inches and a wall thickness of 1/2 inch and having a length of about 37Vfeet (two 20-inch casings welded together) was fitted above the initial casing and welded thereto. The hammer was engaged and the second joint of casing was driven into the ground in about two minutes. Thereafter, a third joint of casing which was about 42 feet in length was installed and welded to the top of the second casing. The hammer was again actuated and this casing required about 20 minutes to drive into the ground. A fourth joint of casing having a length of 43 feet was welded to the top of the third casing and again driven into the ground. The first 22 feet required 11 minutes. Thereafter, a short-jointed casing (about 22 feet in length) was welded to the top of the fourth joint and about 5 feet of the Casin-g was driven in about 47 minutes. Thereafter, about 3 feet was driven in 74 minutes. At this point the rate of penetration slowed down to about one inch in 5 minutes. The resulting casing depth was 154 feet.

The hammer then was disconnected and an 18-inch diameter drill was set up to clean out the earth core Iwithin the casing. The drill was then lowered until all of the earth was withdrawn from the well casing and the drill was used to drill an 18-inch hole to a depth of 209 feet where it penetrated a dense lime strata. Thereafter, the drilling rig was removed from the hole and a piece of casing (about l2 feet) was Welded to the top of the exposed casing. The 12-foot joint required 47 minutes to drive. Thereafter, a final joint of casing, measuring about 41 feet, was welded to the top of the l2-foot casing and the hammer actuated. The total ldriving time for the 41- foot casing was about 100 minutes. At a depth of about 205 feet, driving of the casing was halted. Thereafter, the 18-inch drilling rig was set up andthe interior of the casing was cleaned out. Drilling proceeded further with the 18-inch drill to provide a hole below the bottom of the casing for mining operations. A water-jet, mining tool was installed and the Well pressured with air up to to p.s.i.g. No leakage of air pressure was observed for 8 hours. Thereafter, mining operations were started and granular phosphate ore was recovered from the mine.

The driving time required per section of well as the cumulative driving time for the entire well is set forth in Table 1. In addition, the type of soil in which the Well was dug is also set forth in Table 1.

6 TABLE I cluding what is considered to represent the best emv l bodiment of the invention. However, it should be clearly W understood that, Within the scope of the appended claims, Depth Cumun the invention may 'be practiced by those skilled in the (feet) Per Section lame S011 stumme 5 art, and having the benefit of this disclosure otherwise 0 less than 0 Siity Clay and Shell. than as specically described and exemplified herein.

one min. Il Sand and Silt. What We daim is:

l Black silt and Shen' 1. Process of sinking a Well for use in the well mining T of granular ore wherein a well casing is in a pressure- 2 10 tight relationship to the earth formation which comprises driving an open-end casing into the ground by driving l 2+ Clay: Sand and Shen means until said casing contacts at least one hard stratum, drilling out the earth core Within said casing, containing drilling beyond the core of said casing through I 15 said hard stratum until a drill ho-le has been bored therel 22+ Ogg' Sand and Mmm Shen through, driving said casing through said drill hole in at yeis.

least one of said hard stratum by said driving means until a granular ore area has been reached.

2. Process of claim 1 wherein said granular ore is a 36 @myy Sand and Mmm P205' 20 phosphorous-containing granular ore. v u 3. Process of claim 1 wherein said driving means l 58+ utilizes sonic vibrations to drive said open-end casing.

45 104+ References Cited *74 178+ 25 UNITED STATES PATENTS 47 823,749 6/1906 Wanner 175--76X L 225+ Dense Clay, Sand and P205. 1,896,111 2/1933 Simmons 175-57 X M 2,720,381 10/1955 Quick 175-67X 1 0 l L del (i l 30 2,975,846 3/1961 Bodine 175-19 l Sl il, In I 10 S a el' 8 100 ngboutmggfget Y 3,289,420 12/1966 Guy 175-67 x 3,297,362 l/l967 Currier 175-67 200 l sfmamme, mi @my (www- 3,311,414 3/1967 Campoli er ai. 2998x 325+ ouslayer) and P101. 3,379,262 4/ 1968 Bodine 175-19 210 Dense Lime (impervious layer). 35 3,384,188 5/1968 Bodme 175-57 X ggg- Clay, Sendand12O5Si1tBeds. 3,393,013 7/1968 Hammer et al. 299-17 2402212221211:

* Drilled .Ahead to 209 Feet.

Pursuant to the requirements of the patent statutes, 40 the principle of this invention has been explained and exemplied in a manner so that it can be readily prac- ERNEST R. PURSER, Primary Examiner R. E. FAVREAU, Assistant Examiner U.S. Cl. X.R. 299--3 ticed 'by those skilled in the art, such exemplication in- 

